Fractured reservoir simulation

ABSTRACT

Simulating fluid flow in a fractured reservoir includes generating a grid for a fractured reservoir model that includes a fracture and a matrix to obtain a generated grid. Cross-flow equilibrium elements are generated based on the generated grid. A volume expansion parameter is selected for the cross flow equilibrium elements, and used, along with physical properties, pore volume and transmissibility multipliers. The physical properties are included in the cross flow equilibrium elements. A fluid flow in the fractured reservoir model is simulated using the pore volume and transmissibility multipliers and a fracture relative permeability curve to obtain a result, which is presented. The fluid flow is calculated for the cross flow equilibrium elements.

CROSS REFERENCE TO RELATED APPLICATIONS

The referenced application claims benefit of U.S. Patent ApplicationSer. No. 62/501,061 filed on May 3, 2017. U.S. Patent Application Ser.No. 62/501,061 is incorporated herein by reference in its entirety.

BACKGROUND

Computer systems are used for a variety of technological fields in orderto model various aspects of a technology. For example, one use ofcomputer systems is to model underground formations and model theextraction of hydrocarbons. Specifically, sensors at the oilfield gatherlarge volumes of data. The sensors send the large volumes of data to thecomputer system. Through the various techniques of mathematical modelingand simulations, the computer system attempts to create an optimaldesign for extracting hydrocarbons. A challenge exists to manage theamount of data that the computer system receives, the execution times,and the various timing requirements for returning a result. Often, thecomputer system is inefficient or inaccurate when performing themodeling and generating a result. Inefficiency causes delay or morecomputing resources to be used and inaccuracy causes the resultingdesign to be non-optimal.

SUMMARY

In general, one or more embodiments is directed to simulating fluid flowin a fractured reservoir. Simulating fluid flow in a fractured reservoirincludes generating a grid for a fractured reservoir model that includesa fracture and a matrix to obtain a generated grid. Cross-flowequilibrium elements are generated based on the generated grid. A volumeexpansion parameter is selected for the cross-flow equilibrium elements,and used, along with physical properties, pore volume andtransmissibility multipliers. The physical properties are included inthe cross-flow equilibrium elements. A fluid flow in the fracturedreservoir model is simulated using the pore volume and transmissibilitymultipliers and a fracture relative permeability curve to obtain aresult, which is presented. The fluid flow is calculated for thecross-flow equilibrium elements.

Other aspects of the invention will be apparent from the followingdescription and the appended claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a schematic view, partially in cross section, ofhydrocarbon production fields in which one or more embodiments may beimplemented.

FIG. 2 shows a well system where a fracking operation is executed.

FIG. 3 shows a diagram of a system in accordance with one or moreembodiments.

FIGS. 4.1 and 4.2 show a flowchart in accordance with one or moreembodiments.

FIGS. 5, 6.1, 6.2, 6.3, 6.4, 7, 8.1, 8.2, 9, 10, 11, 12, 13, 14, and 15show examples in accordance with one or more embodiments.

FIGS. 16.1 and 16.2 show a computing system in accordance with one ormore embodiments.

DETAILED DESCRIPTION

Specific embodiments will now be described in detail with reference tothe accompanying figures. Like elements in the various figures aredenoted by like reference numerals for consistency.

In the following detailed description of embodiments, numerous specificdetails are set forth in order to provide a more thorough understanding.However, it will be apparent to one of ordinary skill in the art thatembodiments may be practiced without these specific details. In otherinstances, well-known features have not been described in detail toavoid unnecessarily complicating the description.

Throughout the application, ordinal numbers (e.g., first, second, third,etc.) may be used as an adjective for an element (i.e., any noun in theapplication). The use of ordinal numbers is not to imply or create anyparticular ordering of the elements nor to limit any element to being asingle element unless expressly disclosed, such as by the use of theterms “before”, “after”, “single”, and other such terminology. Rather,the use of ordinal numbers is to distinguish between the elements. Byway of an example, a first element is distinct from a second element,and the first element may encompass more than one element and succeed(or precede) the second element in an ordering of elements.

In general, embodiments are directed to improving accuracy andefficiency of a computer system when simulating fluid flow in afractured reservoir. One or more embodiments perform numeric simulationof reservoir models. In one or more embodiments, the reservoir may be atight reservoir. For example, the tight reservoir may be a shaleformation that contain hydrocarbon fluids (e.g. oil and gas). One ormore embodiments may be applied to reservoir simulation to manage aphysical reservoir. Reservoir simulation involves the construction of acomputer model to represent a portion of a subsurface formation (e.g., areservoir) for the purposes of making decisions regarding thedevelopment of an oil and gas field.

The tight reservoirs may be difficult to develop as the reservoirformation exhibits very low permeability (e.g., microDarcy or nanoDarcyorders of magnitude) that reduces the flow of hydrocarbon fluids towardthe production wells. In one or more embodiments, the tight reservoirsmay be artificially fractured in order to create high permeabilitypathways for the hydrocarbon fluids to reach the production wells. Inone or more embodiments, the fracture space creates large difference ofrock properties between the fracture and the rock matrix. The largevariation of rock properties across fractures complicates theapplicability of traditional simulation of hydrocarbon storage andtransport in pores.

One or more embodiments may provide a method and system for simulationof fluid transport in fractured reservoirs by analyzing the impact offracture-matrix fluid mobility on flow behavior using an efficientgeneral purpose field-scale fractured (EGPFSF) reservoir simulationmodel. In one or more embodiments, the EGPFSF model is obtained bycombining hybrid grid model with a cross flow equilibrium (CFE) model.The EBPFSF reservoir simulation model may be referred to as HG-CFEmodel.

In particular, one or more embodiments are directed to efficientlysimulating a reservoir, such as a tight reservoir, on a computer system.Because of the number of calculations performed using single porosity(SP) simulation, SP simulation may be considered inefficient whenexecuting on a computer system, while other reservoir simulationtechniques may not be sufficiently accurate. Because of the decrease inexecution time through fewer computations, one or more embodimentsincreases the performance of the computing system while adhering to adesired level of accuracy.

The hybrid grid (HG) model represents fractures as lower-dimensionalobjects that still are represented as cells in the computational grid.The HG model is equivalent to a SP model with the advantage of providinga solution for the small control volumes at the intersection betweenfractures. However, the simulation run time is constrained by theinternal small fracture cells (i.e., small pore volumes) characterizedwith high permeability.

In one or more embodiments, the cross-flow equilibrium model includescombining fractures with a fraction of the neighboring matrix blocks oneither side of the fractures into larger elements to achieve a bettercomputational efficiency over conventional SP models. The implementationof CFE in the field is dependent on an accurate computational gridassociated with the CFE elements. The EGPFSF model improves the CFEmodel by analyzing the impact of fracture-rock matrix flow interaction.The HG-CFE model, may configured to be implemented on both structuredand unstructured meshes.

In one or more embodiments, the HG-CFE model is implemented as acomputer model to simulate fluid flow in fracture and rock matrix. Thecomputer model represents the physical space of the reservoir by anarray of discrete grid blocks. The physical space is delineated by agrid which may be structured or unstructured. Each block in the gridrepresents a subsurface volume. The array of grid blocks may betwo-dimensional (2D), three-dimensional (3D), etc. Values for physicalproperties, such as porosity, permeability and water, oil, and gassaturation, may be associated with each grid block. The value of eachattribute is implicitly deemed to apply uniformly throughout the volumeof the reservoir that is represented by the grid block. As an example,simulations may solve a complex set of non-linear partial differentialequations that model the fluid flow in porous media over a sequence ofsimulation time points. Grid resolution may impact the accuracy ofsimulation results, such as in unstable displacement processes. In oneor more embodiments, upscaling techniques may be used to capture finescale phenomena while improving the computation time.

FIG. 1 depicts a schematic view, partially in cross section, of anonshore field (101) and an offshore field (102) in which one or moreembodiments may be implemented. In one or more embodiments, one or moreof the modules and elements shown in FIG. 1 may be omitted, repeated,and/or substituted. Accordingly, embodiments should not be consideredlimited to the specific arrangement of modules shown in FIG. 1 .

As shown in FIG. 1 , the fields (101), (102) includes a geologicsedimentary basin (106), wellsite systems (192), (193), (195), (197),wellbores (112), (113), (115), (117), data acquisition tools (121),(123), (125), (127), surface units (141), (145), (147), well rigs (132),(133), (135), production equipment (137), surface storage tanks (150),production pipelines (153), and an exploration and production (E&P)computer system (180) connected to the data acquisition tools (121),(123), (125), (127), through communication links (171) managed by acommunication relay (170).

The geologic sedimentary basin (106) contains subterranean formations.As shown in FIG. 1 , the subterranean formations may include severalgeological layers (106-1 through 106-6). As shown, the formation mayinclude a basement layer (106-1), one or more shale layers (106-2,106-4, 106-6), a limestone layer (106-3), a sandstone layer (106-5), andany other geological layer. A fault plane (107) may extend through theformations. In particular, the geologic sedimentary basin includes rockformations and may include at least one reservoir including fluids, forexample the sandstone layer (106-5). In one or more embodiments, therock formations include at least one seal rock, for example, the shalelayer (106-6), which may act as a top seal. In one or more embodiments,the rock formations may include at least one source rock, for examplethe shale layer (106-4), which may act as a hydrocarbon generationsource. The geologic sedimentary basin (106) may further containhydrocarbon or other fluids accumulations associated with certainfeatures of the subsurface formations. For example, accumulations(108-2), (108-5), and (108-7) associated with structural high areas ofthe reservoir layer (106-5) and containing gas, oil, water or anycombination of these fluids.

In one or more embodiments, data acquisition tools (121), (123), (125),and (127), are positioned at various locations along the field (101) orfield (102) for collecting data from the subterranean formations of thegeologic sedimentary basin (106), referred to as survey or loggingoperations. In particular, various data acquisition tools are adapted tomeasure the formation and detect the physical properties of the rocks,subsurface formations, fluids contained within the rock matrix and thegeological structures of the formation. For example, data plots (161),(162), (165), and (167) are depicted along the fields (101) and (102) todemonstrate the data generated by the data acquisition tools.Specifically, the static data plot (161) is a seismic two-way responsetime. Static data plot (162) is core sample data measured from a coresample of any of subterranean formations (106-1 to 106-6). Static dataplot (165) is a logging trace, referred to as a well log. Productiondecline curve or graph (167) is a dynamic data plot of the fluid flowrate over time. Other data may also be collected, such as historicaldata, analyst user inputs, economic information, and/or othermeasurement data and other parameters of interest.

The acquisition of data shown in FIG. 1 may be performed at variousstages of planning a well. For example, during early exploration stages,seismic data (161) may be gathered from the surface to identify possiblelocations of hydrocarbons. The seismic data may be gathered using aseismic source that generates a controlled amount of seismic energy. Inother words, the seismic source and corresponding sensors (121) are anexample of a data acquisition tool. An example of seismic dataacquisition tool is a seismic acquisition vessel (141) that generatesand sends seismic waves below the surface of the earth. Sensors (121)and other equipment located at the field may include functionality todetect the resulting raw seismic signal and transmit raw seismic data toa surface unit (141). The resulting raw seismic data may include effectsof seismic wave reflecting from the subterranean formations (106-1 to106-6).

After gathering the seismic data and analyzing the seismic data,additional data acquisition tools may be employed to gather additionaldata. Data acquisition may be performed at various stages in theprocess. The data acquisition and corresponding analysis may be used todetermine where and how to perform drilling, production, and completionoperations to gather downhole hydrocarbons from the field. Generally,survey operations, wellbore operations and production operations arereferred to as field operations of the field (101) or (102). These fieldoperations may be performed as directed by the surface units (141),(145), (147). For example, the field operation equipment may becontrolled by a field operation control signal that is sent from thesurface unit.

Further as shown in FIG. 1 , the fields (101) and (102) include one ormore wellsite systems (192), (193), (195), and (197). A wellsite systemis associated with a rig or a production equipment, a wellbore, andother wellsite equipment configured to perform wellbore operations, suchas logging, drilling, fracturing, production, or other applicableoperations. For example, the wellsite system (192) is associated with arig (132), a wellbore (112), and drilling equipment to perform drillingoperation (122). In one or more embodiments, a wellsite system may beconnected to a production equipment. For example, the well system (197)is connected to the surface storage tank (150) through the fluidstransport pipeline (153).

In one or more embodiments, the surface units (141), (145), and (147),are operatively coupled to the data acquisition tools (121), (123),(125), (127), and/or the wellsite systems (192), (193), (195), and(197). In particular, the surface unit is configured to send commands tothe data acquisition tools and/or the wellsite systems and to receivedata therefrom. In one or more embodiments, the surface units may belocated at the wellsite system and/or remote locations. The surfaceunits may be provided with computer facilities (e.g., an E&P computersystem) for receiving, storing, processing, and/or analyzing data fromthe data acquisition tools, the wellsite systems, and/or other parts ofthe field (101) or (102). The surface unit may also be provided with orhave functionally for actuating mechanisms of the wellsite systemcomponents. The surface unit may then send command signals to thewellsite system components in response to data received, stored,processed, and/or analyzed, for example, to control and/or optimizevarious field operations described above.

In one or more embodiments, the surface units (141), (145), and (147)are communicatively coupled to the E&P computer system (180) via thecommunication links (171). In one or more embodiments, the communicationbetween the surface units and the E&P computer system may be managedthrough a communication relay (170). For example, a satellite, towerantenna or any other type of communication relay may be used to gatherdata from multiple surface units and transfer the data to a remote E&Pcomputer system for further analysis. Generally, the E&P computer systemis configured to analyze, model, control, optimize, or performmanagement tasks of the aforementioned field operations based on thedata provided from the surface unit. In one or more embodiments, the E&Pcomputer system (180) is provided with functionality for manipulatingand analyzing the data, such as analyzing seismic data to determinelocations of hydrocarbons in the geologic sedimentary basin (106) orperforming simulation, planning, and optimization of exploration andproduction operations of the wellsite system. In one or moreembodiments, the results generated by the E&P computer system may bedisplayed for user to view the results in a two-dimensional (2D)display, three-dimensional (3D) display, or other suitable displays.Although the surface units are shown as separate from the E&P computersystem in FIG. 1 , in other examples, the surface unit and the E&Pcomputer system may also be combined. The E&P computer system and/orsurface unit may correspond to a computing system, such as the computingsystem shown in FIGS. 15.1 and 15.2 and described below.

FIG. 2 depicts a fracking operation performed on a subsurface formationat the location of a well system. For example, the well system may bethe well system (193) as presented in FIG. 1 . In one or moreembodiments the fracking operation includes injecting high pressurewater into a low permeability subsurface formation in order to generatea fracture network (205) within the subsurface formation. For example,the subsurface formation may be a shale layer (106-2). In one or moreembodiments, the high pressure injection is executed by a mobile waterpump (201) injecting the water through a wellbore (113) of ahorizontally drilled well. In one or more embodiments, the fracturenetwork (205) enhance the flow of hydrocarbon fluids from the rockmatrix into the wellbore. Other technologies for generating fracturenetworks may be used without departing from the scope of the claims.

FIG. 3 shows more details of the E&P computer system (180) in which oneor more embodiments of the technology may be implemented. In one or moreembodiments, one or more of the modules and elements shown in FIG. 3 maybe omitted, repeated, and/or substituted. Accordingly, embodiments ofthe efficient general purpose field-scale fractured reservoir simulationmodel should not be considered limited to the specific arrangements ofmodules shown in FIG. 3 .

As shown in FIG. 3 , the E&P computer system (180) includes a datarepository (310) for storing input data, intermediate data, andresultant outputs of the analysis data, a modeling tool (330), and afield equipment module (350) for performing various tasks of the fieldoperation. In one or more embodiments, the data repository (310) mayinclude one or more disk drive storage devices, one or moresemiconductor storage devices, other suitable computer data storagedevices, or combinations thereof. In one or more embodiments, contentstored in the data repository (310) may be stored as a data file, alinked list, a data sequence, a database, a graphical representation,any other suitable data structure, or combinations thereof.

In one or more embodiments, the content stored in the data repository(310) includes hydraulic transport properties (311), grid blocks (313),reservoir model (315), scaling factors (317) and fluid fluxes (319).Each of these components is discussed below.

In one or more embodiments, the hydraulic transport properties (311)describe the physical properties of fluids and rocks of the subsurfaceformation. In one or more embodiments, the hydraulic transportproperties (311) control the flow velocity of hydrocarbon components andphases through the rocks of the subsurface formations. For example, thefluid properties may include density, viscosity, temperature, pressure,chemical composition, and other properties of one or more fluids.Further, the rock properties may include density, porosity,permeability, capillary entry pressure and other properties of one ormore rocks. In one or more embodiments, the rocks may be naturally orartificially fractured. The fractures may be characterized by the faultproperties (e.g., capillary pressure, shale gauge ratio, etc.)associated with the subsurface formations.

In one or more embodiments, the subsurface reservoir can be representedin a computer model as a grid. A grid is a mathematical construction ofa volume of rock representing a fractured reservoir model and thecharacteristics that form the reservoir. A grid includes grid blocks(313), each grid block corresponding to a subsurface volume of thereservoir. In one or more embodiments, each grid block is characterizedby a set of location and dimension properties. In one or moreembodiments, the grid block dimension parameters may result from themodel resolution parameter. In one or more embodiments, the grid blocksmay be structured, or defined by a regular shape. In one or moreembodiments, the grid blocks may be unstructured, or defined by anirregular shape. In one or more embodiments, each grid block hasassigned a set of hydraulic transport properties (311) that are constantwithin a single grid block.

The fractured reservoir model (315) is representations of the subsurfacedomains that includes spatial description of subsurface components andcomponents physical properties. The fractured reservoir model includes(e.g., represents) one or more fractures and one or more matrices. Afracture is any separation in a geologic formation, such as a joint or afault that divides the rock into two or more pieces. The fracture existsas a separation within the matrix, where the matrix is the rock.Fractures may be naturally occurring through tectonic forces, fluidmovement, and chemical dissolution or fractures may be the result offorcing fluids or slurries into underground formations through theprocess of hydraulic fracturing. In one or more embodiments, thefractured reservoir model is a bifurcated system having a grid space anda computational space.

In the grid space, the fractured reservoir model is a grid having gridblocks (313). Each grid block has associated hydraulic transportproperties (311), boundary conditions and other elements used tosimulate the reservoir model. The grid blocks represent matrix elements.Fractures are represented in a lower dimension than the grid blocks andare between grid blocks according to the fractured reservoir. Forexample, if the grid blocks are in three dimensional space, thefractures are in two-dimensional space. By way of another example, ifthe grid blocks are in two-dimensional space, the fractures are inone-dimensional space between various grid blocks.

In the computational space, the fractured reservoir model has the gridblocks for both the matrix and the fractures, where the matrix and thefractures represented in the same dimension. For example, if the gridblocks are in three dimensional space, the fractures are inthree-dimensional space. By way of another example, if the grid blocksare in two-dimensional space, the fractures are in two-dimensional spacebetween various grid blocks. The grid blocks corresponding to the matrixis represented as matrix elements.

In the computational space, the fractured reservoir model includes a setof cross flow equilibrium elements. A cross flow equilibrium element isan expanded fracture that not only includes the actual fracture volume,but also incorporates a portion of the surrounding rock into thefracture volume. Specifically, with a tight reservoir, an accurate modelof the fracture represents the fracture as a small volume in betweenmatrix elements, where small is relative to the size of the surroundingmatrix elements. Because of the relative size of the fracture ascompared to the matrix elements, simulations of fluid fluxes usingaccurate models take a substantial amount of compute time by a computingsystem. One or more embodiments artificially expands the size of thefracture to include a portion of the surrounding matrix elements alongthe length of the fracture. The matrix elements around the fracture arereduced correspondingly in size. The result of using larger cross flowequilibrium elements corresponding to larger control volumes for thefracture. Thus, one or more embodiments achieve a better computationalefficiency than conventional fractured reservoir computational gridmodels.

Continuing with the reservoir model, in one or more embodiments, thefracture to fracture intersection does not include a volume. In otherwords, the fracture to fracture intersection is not modeled inaccordance with one or more embodiments of the invention. Rather, a stardelta approach is used to model fluid flow between fractures.

In one or more embodiments, a volume expansion parameter is the amountthat the fracture is expanded to include the surrounding matrixelements. The volume expansion parameter may be an absolute value (e.g.,a defined value of a minimum size or set size) or a multiplier thatdefines a value to multiply by the fracture size. Other type of volumeexpansion parameters may be used without departing from the scope of theclaims.

The scaling factors (317) are constant values applied to physicalproperty to obtain an equivalent property that would produce the sameresults in a simplified calculation as the results of a complexcalculation using the physical property. In one or more embodiments, thescaled physical property is proportional with the physical property. Theproportionality constant or amount that the scaled physical property isproportional with the physical property is the scaling factor. Forexample, the hydraulic transmissivity used to predict a set of fluidfluxes may be scaled to be used with a simpler version of fluid flowequation.

The fluid fluxes (319) are defined as fluxes of the fluids crossing thegrid block boundaries as resulted from reservoir simulations. A flux isa flow rate per unit area. In one or more embodiments, a set of fluidfluxes are calculated at each time step during a reservoir simulation.

Continuing with FIG. 3 , the E&P computer system (180) additionallyincludes a modeling tool (330) in accordance with one or moreembodiments. The modeling tool (330) includes a user interface (331), amodel builder (333), and a model simulator (335). Each of thesecomponents is described below.

In one or more embodiments, the user interface (331) corresponds to agraphical user interface (GUI) that includes functionality to receiveinput from a user and present or display graphical data to the user. Theuser interface (331) may include a 3D subsurface reservoir viewer, a 2Dsection of subsurface reservoir profile viewer, and parameters valueinput fields in accordance with one or more embodiments. The inputfields include functionality to receive input parameters from a user.For example, the input parameters may include a set of boundaryconditions to simulate a model, a gridding option to grid a reservoirmodel, an observation point angle defining a rendering of the 3Dsubsurface reservoir, a location to display a 2D section of subsurfacereservoir, a color palette to map different hydraulic transportproperties, or any other parameter for simulating the reservoir. In oneor more embodiments, the input fields may include selection boxes, textfields, drop-down menus, or any other type of field for a user to inputdata.

The model builder (333) is a software tool configured to build areservoir model (315) defined by the grid blocks (313). In one or moreembodiments, the model builder (333) is configured to divide asubsurface reservoir volume into grid blocks according to a griddingmodel. In one or more embodiments, the model builder is configured togenerate the fracture volumes and assign specific grid blocks to thefracture volumes. In one or more embodiments, the model builder isconfigured to assign hydraulic transport properties to each grid blocks.In one or more embodiments, the hydraulic transport properties may bespecific to grid blocks included in fracture volumes and to grid blocksincluded in rock matrix volumes.

The model simulator (335) is a software tool configured to simulate areservoir model (315). In one or more embodiments, the model simulatoris configured to calculate the fluid flow of fluids, such as oil, water,and gas, through porous space of a subsurface reservoir and into thewellbores. In one or more embodiments, the model simulator (335)simulates the fractured reservoir model to produce a set of values forthe fluid fluxes (319). In one or more embodiments, the model simulatormay be a numeric simulator, the numeric simulator solves the fluid flowequations using numeric methods applied on a discrete reservoir model.In one or more embodiments, the model simulator is configured tosimulate fluid transport through the grid blocks (313) using fluidtransport laws based on conservation of mass, momentum and energyequations with applied boundary conditions. In one or more embodiments,the model simulator may be a multi-phase compositional simulator.

The field equipment module (350) is configured to generate a fieldoperation control signal based at least on a result generated by the E&Pcomputer system (180), such as based on the fluid hydrocarbon productionestimate from a reservoir simulation. As noted above, the fieldoperation equipment depicted in FIG. 1 may be controlled by the fieldoperation control signal. For example, the field operation controlsignal may be used to control drilling equipment, an actuator, a fluidvalve, or other electrical and/or mechanical devices disposed about thefields (101) and (102). In one or more embodiments, field equipmentmodule (350) is configured to acquire a set of data from the fieldregarding one or more properties of the subsurface formations.

While FIG. 3 shows a configuration of components, other configurationsmay be used without departing from the scope. For example, variouscomponents may be combined to create a single component. As anotherexample, the functionality performed by a single component may beperformed by two or more components.

FIG. 4.1 and FIG. 4.2 show flowcharts in accordance with one or moreembodiments. While the various blocks in these flowcharts are presentedand described sequentially, one of ordinary skill will appreciate thatat least some of the blocks may be executed in different orders, may becombined or omitted, and at least some of the blocks may be executed inparallel. Furthermore, the blocks may be performed actively orpassively. For example, some blocks may be performed using polling or beinterrupt driven in accordance with one or more embodiments. By way ofan example, determination blocks may not use a processor to process aninstruction unless an interrupt is received to signify that conditionexists in accordance with one or more embodiments. As another example,determination Blocks may be performed by performing a test, such aschecking a data value to test whether the value complies with the testedcondition in accordance with one or more embodiments.

FIG. 4.1 shows a flowchart for simulating fluid flow in a fracturedreservoir in accordance with one or more embodiments. In one or moreembodiments, the flowchart in FIG. 4.1 presents an HG-CFE modelimplementation.

In Block 453, a grid is generated for a fractured reservoir model thatincludes a fracture and a matrix. A virtual grid that spans thefractured reservoir and partitions the volume of the fractured reservoiris defined, such that each grid block in the virtual grid has acorresponding location in the fractured reservoir. Further, eachlocation in the fractured reservoir has a corresponding grid block.Values of physical properties are assigned to the grid blocks using thedata acquisition tools deployed across the fields as depicted in FIG. 1above. In particular, the data acquisition tools may obtain some of thevalues directly. Other values may be calculated based on the obtainedvalues.

In Block 455, a volume expansion parameter is selected for the crossflow equilibrium elements. A default value that is preconfigured may beused for the volume expansion parameter. By way of another example, thevolume expansion parameter may be received via a user interface orapplication programming interface.

In Block 456, cross flow equilibrium elements are generated based on thegenerated grid and the volume expansion parameter. The generated griddefines the locations of the fractures and the matrix elements in thecomputational space. The actual volumes of the fractures may bedetermined based on data acquired using the data acquisition toolsdescribed above with reference to FIG. 1 . The fractures are expanded insize according to the volume expansion parameter. In particular thevolume expansion parameter defines the amount that the fracture isexpanded. In one or more embodiments, the fracture is expanded inequidistant amount in each direction, from the actual fracture volume,as defined by the volume expansion parameter.

In Block 457, pore volume and transmissibility multipliers arecalculated, using physical properties for the plurality of CFE elements.In one or more embodiments, the pore volume multiplier and thetransmissibility multiplier is calculated based on a percentage of theCFE element that is matrix and the percentage of the CFE element that isfracture. The percentage of the CFE element that is matrix is multipliedby the pore volume and transmissibility multiplier of the matrix toobtain a first result. The percentage of the CFE element that isfracture is multiplied by the pore volume multiplier of the fracture toobtain a second result. The first result and the second result arecombined, such as summed, respectively, to obtain the pore volume andtransmissibility multipliers, respectively, for the CFE element. Thus,the CFE element has pore volume and transmissibility multipliers that isa combination of the pore volume and transmissibility multipliers forthe matrix and fracture. In one or more embodiments, the pore volume andtransmissibility multipliers are defined for physical properties of theCFE element. For example, the pore volume and transmissibilitymultipliers may be defined for volume, porosity, permeability,net-to-gross, gas, oil, water and transmissibility.

In Block 461, fluid flow is simulated in the fractured reservoir modelusing the pore volume and transmissibility multipliers and a fracturerelative permeability curve to obtain a result. The fluid flow iscalculated for the cross-flow equilibrium elements. The fluid flow mayalso be calculated across the matrix elements and between CFE elements.Because the pore volume and transmissibility multipliers beingcalculated using both the physical properties of the matrix and thefracture, fluid flow across a CFE element accounts for the fact that theCFE element represents a combination of fracture and matrix.

The fluid flow between CFE elements may be calculated using a star deltaapproach. Specifically, a CFE element may connect at a single point toat least two other CFE element (e.g., in a star pattern having a centerpoint of intersection). The fluid flow between any two of the joiningCFE elements is the deemed the same as if the CFE elements wereconnected as a triangle (e.g., delta) without the central intersection.Thus, fluid flow between CFE elements is calculated as if the CFEelements were arranged in a delta pattern.

In the case of a constant fracture aperture and an isotropic medium, theCFE element to CFE element, may be estimated as a weighted average ofthe fracture and matrix relative permeability curves. For example, thephase relative permeability may be calculated using the followingequation, Eq. 1.

$\begin{matrix}{k_{{r\;\alpha},{CFE}} = {{\left( {1 - {a\text{/}A}} \right)\frac{K_{m}}{K_{f}}k_{{r\;\alpha},m}} + {\left( {a\text{/}A} \right)k_{{r\;\alpha},f}}}} & \left( {{Eq}.\mspace{14mu} 1} \right)\end{matrix}$In equation Eq. 1, k_(rα,CFE) is the fracture relative permeability ofthe CFE element, α is the size of the fracture aperture, A is the areaof the crossflow element, Km is the absolute permeability of the matrixelement, K_(f) is the absolute permeability of the fracture, k_(rα,m) isthe relative permeability of the matrix, and k_(rα,f) is the relativepermeability of the fracture.

The fluid flow from a fracture to a matrix may be calculated using thefracture relative permeability curve of the fracture. In other words,the relative permeability of the fracture rather than the relativepermeability of the matrix may be used to calculate fluid flow.

The simulations calculate the path and rate of fluid flows through thetight reservoir. From the simulations, information about the compositionof fluid, timing for hydrocarbon, and other information may bedetermined. The result that is calculated may be a dynamic resultshowing changes over time, and/or a static result that providesinformation for a single point in time.

In Block 463, the result is presented. The result may be presented toanother application, such as using an application programming interface,placed in storage, using a graphical user interface, or via anotherpresentation technique. In one or more embodiments, the result ispresented to a user via a user interface in the surface unit depicted inFIG. 1 above. In one or more embodiments, the result is presented bysending to a software and/or hardware component of the exploration andproduction (E&P) computer system or wellsite systems depicted in FIG. 1above.

A field operation may be performed in response to presenting the packerposition and choking parameter. In one or more embodiments, the fieldoperation is performed as described in reference to FIG. 1 above.

FIG. 4.2 shows a flowchart for calculating fluid fluxes in accordancewith one or more embodiments. One or more blocks of FIG. 4.2 may beadded to and/or replace one or more blocks of FIG. 4.1 . In Block 400, aset of hydraulic transport properties are read from memory. In Block401, a set of fractures are generated. In one or more embodiments, thefracture space is associated with a set of grid blocks with small volumeand high porosity.

In Block 402, a set of grid blocks are generated using a hybrid gridmesh. In one or more embodiments, a model builder generates the gridblocks by dividing the reservoir volume using a regular mesh, anirregular mesh or any combination of meshes. In one or more embodiments,the model builder may use a mesh to generate grid blocks for rock matrixvolume and a different mesh for fractures volume.

In Block 403, a pore volume scaling factor is selected. In Block 404, afracture hydraulic transmissivity scaling factor is selected. In Block405, a test is performed to determine if the fracture aperturedistribution is isotropic. In one or more embodiments, a fractureaperture is considered isotropic is the changes in hydraulic transportproperties are equal in various directions.

In Block 406, if the fracture aperture distribution is isotropic, ascaled CFE-CFE relative permeability is calculated for each block. Forexample, the scaled CFE-CFE relative permeability may be calculatedusing the above equation, Eq. 1.

In Block 407, if the fracture aperture distribution is not isotropic, afracture relative permeability is calculated transversal to CFE for eachblock. In one or more embodiments, fractures grid blocks are combinedwith a small fraction of the rock matrix grid blocks on either side ofthe fracture in order to generate combined grid blocks.

In Block 408, the fluid fluxes across blocks are calculated based onrelative permeability. In one or more embodiments, the model simulatorcalculates fluxes by integrating the appropriate fluxes for the rockmatrix grid blocks and fracture grid blocks.

In Block 409, the fluid fluxes are presented. For example, the fluidfluxes may be presented as described above with respect to Block 463 inFIG. 4.1 .

FIG. 5 shows a portion of a fractured reservoir divided into gridblocks. In one or more embodiments, the grid blocks (501) are shadedaccording to a shaded map scale that represent the value of a hydraulictransport property. As seen in FIG. 5 , the grid blocks associated withthe rock matrix (501) have large difference in hydraulic transportproperty than the grid blocks associated with the fractures (503). Inone or more embodiments, the grid blocks associated with the fractures(503) are connected with the wellbore (505) facilitating transfer offluids between the reservoir and the wellbore.

The fracture network topology and the high contrast between fracture andmatrix properties may be very challenging during a simulation process.Different types of models are used to represent tight reservoir. Forexample, FIG. 6.1 illustrates single porosity (SP) model (600) in twodimensional space. The matrix blocks are adjacent to the fractures. Thematrix block represents rock space. At the intersection of thefractures, a small fracture pore volume exists. Due to the contrast inmatrix/fracture properties, numerical simulations are computationallyvery expensive in the single porosity model.

FIG. 6.2 illustrates a hybrid grid model (602). In the hybrid gridmodel, grid blocks from different dimensional spaces are combined. Thehybrid grid model uses two spaces: (i) a grid space where the fracture'sdimension is reduced by 1 (604), and (ii) a computational space wherethe matrix and fractures are drawn in the same dimension (606). In thehybrid grid, the point at the intersection (denoted in FIG. 6.1 as ablack dot), is removed. In other words, a control volume is not added tothe fracture intersection in the model to consider the fracture tofracture intersection.

FIG. 6.3 illustrates a CFE model (608). In both the single porosity andhybrid grid models, different pressures are calculated in the fractureand adjacent matrix cells. To achieve computational efficiency, the CFEmethodology combines fractures with a small fraction of the matrixblocks on either side in larger computational elements using theassumption that a large permeability, but small pressure gradient acrossthe fracture-matrix interface results in a transverse flux thatinstantaneously equilibrates the fracture fluid with the fluidimmediately next to it in the matrix.

FIG. 6.4 shows a HG-CFE model (610) in accordance with one or moreembodiments. In the HG-CFE model, the combined fracture-matrix elementsmay be denoted as CFE elements (614). The fluxes across the edges of theCFE elements may be determined by integrating the appropriate Darcyfluxes for the matrix and fracture contributions. The CFE treatment offractures allows coarser grids, which translates into large CFLtime-steps and increased computational efficiency. The efficiency of thepressure update is also improved, because of the lower contrast in CFfracture and matrix permeabilities. As shown in model (612), a largercontrol volume is created to calculate contribution from the fractureand the matrix. A larger control volume means that simulations may nolonger be performed with small fractures (e.g., the pore volume islarger.).

One or more embodiments may provide for the integration of flowequations in the CFE elements related to fracture-fracture flow. Forfracture-matrix interaction, the relative permeability of the fractureis used to calculate the flow from the fracture to the matrix. Using ageneral purpose finite volume simulator, a sensitivity analysis withrespect to the relative permeability curve is performed to calculate thefracture-matrix flow. Using the fracture relative permeability curveprovided an accurate approximation as the flow is initiated from thecenter of the control volume, with the CFE element assumed symmetricwith respect to the topology of the fracture. While the relativepermeability of the matrix for flow from fracture to matrix may be usedwith a CFE method, embodiments herein may use the fracture relativepermeability curve (relative permeability of the fracture) instead ofthe relative permeability of the matrix.

In one or more embodiments, the fracture network is gridded using lowerdimensional fractures as shown in model (616). Then, the cross-flowequilibrium elements properties are determined in the computationalspace as shown in model (612). As shown, complex fracture networks arehandled as gridding of lower dimensional fractures. Computation speed isincreased (fewer time-steps) as the cross flow equilibrium applicationis applied in the computational space, thereby eliminating the grideffect. Fracture volume expansion is calculated exactly withoutincluding the expansion in the grid space. Running sensitivity analysiswith respect the volume of the expanded fractures (i.e. volume of theCFE elements) is efficient, as re-gridding of the fractured system isnot performed in one or more embodiments.

Expanding the fracture cells volume through CFE concept is associatedwith pore volume and transmissibility changes in the fracture system. Ifthe CFE elements are designed explicitly in the grid space, thesimulator may handle the pore volume calculation, in proportion, andbased on the fracture and matrix properties. The transmissibilitycalculation between CFE elements is straight forward performed given thearea open to flow from both original fracture and matrix parts insidethe CFE element.

As shown, the CFE elements do not show up in the grid space andcalculations are performed in the computational space using the exactexpressions. A grid of fractured reservoirs may be generated, using onedimensional fractures in two dimensional reservoirs, and two dimensionalfractures in three dimensional reservoirs.

FIG. 7 shows an example of expanding a fracture to create a CFE element.In FIG. 7 , the fracture and the CFE element are two dimensional. Thefracture (702) has an area a. The fracture volume expansion parameter Ais selected as shown in FIG. 7 and use to create CFE element 704 ofhaving an area of A. Based on the value of A, pore volume andtransmissibility multipliers are calculated using both the fracture andmatrix properties in the CFE elements.

The following is an example set of equations that may be used tocalculate fluid flow using the HG-CFE method. In one or moreembodiments, the fluid flow mathematical description is based on theprinciple of mass conservation that is the accumulation of mass in somedomain that is exactly balanced by the mass flowing through the boundaryof the domain and the contribution of sources/sinks within the domain.The material balance equation for component i is given by equations, Eq.2 and Eq. 3.

$\begin{matrix}{{{\frac{\partial M_{i}}{\partial t} + {\nabla{.U_{i}}}} = F_{i}},{i = 1},n_{c},{where},} & \left( {{Eq}.\mspace{14mu} 2} \right) \\{U_{i} = {\sum\limits_{\alpha}{x_{i\;\alpha}b_{\alpha}{v_{\alpha}.}}}} & \left( {{Eq}.\mspace{14mu} 3} \right)\end{matrix}$

In the equations Eq. 2 and Eq. 3, n_(c) is the number of components inthe system, the subscripts α and i denote, respectively, the phaseidentity (oil, gas or water), and the component, U, is the molar flux ofcomponent i, b_(α) is the molar density of the phase α, x_(iα) is themole fraction of component i in phase α, and F_(i) is the sink/sourceterm for component i.

Each of the volumetric convective phase fluxes is may be calculatedusing the corresponding Darcy relation in equation Eq. 4.υ_(α)=λ_(α) K(∇p _(α)−ρ_(α) g),α=o,g.   (Eq. 4)in terms of gravitational acceleration g, permeability tensor K,mobility λ_(α) (S_(α)), saturation S_(α), and mass density ρ_(α).

The pressure in the three phases are related by capillary pressures maybe calculated using equations, Eq. 5 and Eq. 6.p _(c)(S _(o))=p _(g) −p _(o),  (Eq.5)p _(c)(S _(w))=p _(o) −p _(w),  (Eq. 6)In equations Eq. 5 and Eq. 6, S_(o) and S_(w) are the saturation of theoil and water phases, respectively. The mole fraction balance impliesthat

$\begin{matrix}{{{\sum\limits_{i = 1}^{n_{c}}\; x_{io}} = 1},{{\sum\limits_{i = 1}^{n_{c}}\; x_{ig}} = 1.}} & \left( {{Eq}.\mspace{14mu} 7} \right)\end{matrix}$

When a component partitions in more than one phase, the thermodynamicequilibrium of the component between phases is determined. Theequilibrium condition for a component that partitions in two phases αand β is that component fugacity in either phase is equal:φ_(iα)=φ_(iβ), for i∈α and i∈β,∀i,α,β  (Eq. 8)where, φ_(iα) and φ_(iβ) are the fugacity of component i in phase α andin phase β, respectively.

To complete the description of the physical model, an initial andboundary conditions are presented below. The initial condition includesthe overall composition and pressure field throughout the domain. Theboundaries are described by non-overlapping Dirichlet and Neumannconditions. Impermeable boundaries may be used, except in productionwells where either a constant pressure or production rate may bedetermined to exist. Injection wells are placed inside the domain assource terms. Production wells can also be described as sink terms, withimpermeable boundaries everywhere.

By way of an example, CFE approximation, equation Eq. 9 may be used. InEquation Eq. 9, below, a is the portion area of a fracture in a CFE ofarea A. The matrix intersecting area is then calculated as A−a. In otherwords, A−a is the matrix intersecting area and shows matrix flow. Thetotal flux for a CFE element ‘i’ (i.e. fracture+matrix) may becalculated as.

$\begin{matrix}{Q_{i,{total}}^{{jk},\tau} = {{Q_{i,m}^{{jk},\tau} + Q_{i,f}^{{jk},\tau}} \approx {{T_{jk}^{m}{\sum\limits_{\alpha}{\left( {\lambda_{\alpha,m}^{\tau}b_{\alpha,m}^{\tau}x_{{i\;\alpha},m}^{\tau}} \right)^{*}\left( {\Phi_{\alpha,m}^{j} - \Phi_{\alpha,m}^{k}} \right)}}} + {T_{jk}^{f}{\sum\limits_{\alpha}{\left( {\lambda_{\alpha,f}^{\tau}b_{\alpha,m}^{\tau}x_{{i\;\alpha},m}^{\tau}} \right)^{*}\left( {\Phi_{\alpha,m}^{j} - \Phi_{\alpha,m}^{k}} \right)}}}}}} & \left( {{Eq}.\mspace{14mu} 9} \right)\end{matrix}$

In equation Eq. (9), T_(jk) denotes the transmissibility constantbetween control volumes j and k. The subscripts f and m refer tofracture and matrix. The variables λ, b, Φ, x, and τ are the phasemobility, molar density, potential, the component mole fraction in therelated phase α, and linear iteration number, respectively. The phasepotential includes the phase pressure and the capillary pressure andgravity forces. The superscript * denotes the upstream direction foreach phase and for each connection.

For non-zero capillary pressure and assuming a same phase pressure inboth fracture and matrix in the cross-flow equilibrium element, thephase potential in the matrix can be calculated using equation Eq. 10.

$\begin{matrix}\begin{matrix}{{\Phi_{\alpha,m}^{j} - \Phi_{\alpha,m}^{k}} =} & {P^{j} - P^{k} - {\frac{1}{2}\left( {\rho_{\alpha}^{j} + \rho_{\alpha}^{k}} \right){g\left( {d^{j} + d^{k}} \right)}} +} \\ & {P_{{c\;\alpha},m}^{j} - P_{{c\;\alpha},m}^{k}} \\{=} & {{\Delta\Psi}^{jk} + {\Delta\; P_{{c\;\alpha},m}^{jk}}}\end{matrix} & \left( {{Eq}.\mspace{14mu} 10} \right)\end{matrix}$Similarly, the phase potential in the fracture may be calculated usingequation, Eq. 11.

$\begin{matrix}\begin{matrix}{{\Phi_{\alpha,f}^{j} - \Phi_{\alpha,f}^{k}} =} & {P^{j} - P^{k} - {\frac{1}{2}\left( {\rho_{\alpha}^{j} + \rho_{\alpha}^{k}} \right){g\left( {d^{j} + d^{k}} \right)}} +} \\ & {P_{{c\;\alpha},f}^{j} - P_{{c\;\alpha},f}^{k}} \\{=} & {{\Delta\Psi}^{jk} + {\Delta\; P_{{c\;\alpha},f}^{jk}}}\end{matrix} & \left( {{Eq}.\mspace{14mu} 11} \right)\end{matrix}$In the above equations, P is the phase pressure, ρ is the phase density,and d is the cell depth.

Replacing Eqs. (10) and (11), in Eq. (9), equations Eq. 12 may be used.

$\begin{matrix}{{\left. {Q_{i,{total}}^{{jk},\tau} = {\sum\limits_{\alpha}{\left( {{T_{jk}^{m}k_{{r\;\alpha},m}^{\tau}} + {T_{jk}^{f}k_{{r\;\alpha},f}^{\tau}}} \right)b_{\alpha}^{\tau}x_{i\;\alpha}^{\tau}\text{/}\mu_{\alpha}^{\tau}}}} \right)^{*}{\Delta\Psi}^{jk}} + {\sum\limits_{\alpha}{\left( {{T_{jk}^{m}k_{{r\;\alpha},m}^{\tau,*}\Delta\; P_{{c\;\alpha},m}^{jk}} + {T_{jk}^{f}k_{{r\;\alpha},m}^{\tau,*}\Delta\; P_{{c\;\alpha},f}^{jk}}} \right)\left( {b_{\alpha}^{\tau}x_{i\;\alpha}^{\tau}\text{/}\mu_{\alpha}^{\tau}} \right)^{*}}}} & \left( {{Eq}.\mspace{14mu} 12} \right)\end{matrix}$

In a specific example of having zero-capillary pressure, the followingequation Eq. 13 may be used.

$\begin{matrix}{\left. {Q_{i,{total}}^{{jk},\tau} = {{Q_{i,m}^{{jk},\tau} + Q_{i,f}^{{jk},\tau}} \approx {\sum\limits_{\alpha}{\left( {{T_{jk}^{m}k_{{r\;\alpha},m}^{\tau}} + {T_{jk}^{f}k_{{r\;\alpha},f}^{\tau}}} \right)b_{\alpha}^{\tau}x_{i\;\alpha}^{\tau}\text{/}\mu_{\alpha}^{\tau}}}}} \right)^{*}{\Delta\Psi}^{jk}} & \left( {{Eq}.\mspace{14mu} 13} \right)\end{matrix}$

The expression in equation Eq. 6 may be written using equation Eq. 14.

$\begin{matrix}{\left. {Q_{i,{total}}^{{jk},\tau} = {{Q_{i,m}^{{jk},\tau} + Q_{i,f}^{{jk},\tau}} \approx {T_{jk}^{f}{\sum\limits_{\alpha}{\left( {{\left( {1 - {a\text{/}A}} \right)\frac{K_{m}}{K_{f}}k_{{r\;\alpha},m}^{\tau}} + \mspace{410mu}{\left( {a\text{/}A} \right)k_{{r\;\alpha},f}^{\tau}}} \right)b_{\alpha}^{\tau}x_{i\;\alpha}^{\tau}\text{/}\mu_{\alpha}^{\tau}}}}}} \right)^{*}{\Delta\Psi}^{jk}} & \left( {{Eq}.\mspace{14mu} 14} \right)\end{matrix}$For isotropic media with constant fracture aperture a, the inputrelative permeability for fracture elements can be scaled according tothe following expression in equation, Eq, 15, to get the relativepermeability for the cross-flow equilibrium elements.

$\begin{matrix}{k_{{r\;\alpha},{CFE}}^{\tau} = {{\left( {1 - {a\text{/}A}} \right)\frac{K_{m}}{K_{f}}k_{{r\;\alpha},m}^{\tau}} + {\left( {a\text{/}A} \right)k_{{r\;\alpha},m}^{\tau}}}} & \left( {{Eq}.\mspace{14mu} 15} \right)\end{matrix}$Furthermore, for isotropic media with constant fracture aperture a, thetotal flow across the CFE elements can be calculated using equation Eq.16.

$\begin{matrix}{Q_{i,{total}}^{{jk},\tau} = {{Q_{i,m}^{{jk},\tau} + Q_{i,f}^{{jk},\tau}} \approx {T_{jk}^{f}{\sum\limits_{\alpha}{\left( {k_{{r\;\alpha},{CFE}}^{\tau}b_{\alpha}^{\tau}x_{i\;\alpha}^{\tau}\text{/}\mu_{\alpha}^{\tau}} \right)^{*}{\Delta\Psi}^{jk}}}}}} & \left( {{Eq}.\mspace{14mu} 16} \right)\end{matrix}$

FIGS. 8.1, 8.2, 9, 10, 11, 12, 13, 14, and 15 show examples ofsimulations in accordance with one or more embodiments. In the examplesin the Figures, the following notation is used. “SP” is a singleporosity model considered as a reference model. “CFE (literature)” iscross-flow equilibrium concept as presented in literature. “CFE (thiswork)” is cross-flow equilibrium concept with fracture to matrix flowbased on the fracture relative permeability set in accordance with oneor more embodiments. “HG-CFE (this work)” is a hybrid grid combined withcross flow equilibrium in accordance with one or more embodiments.Except as described, “CFE (this work)” and “HG-CFE (this work)” methodsherein are using scaled relative permeability curves in the fracture.

Turning to FIGS. 8.1 and 8.2 , the example shown is a comparison ofdiscrete CFE (this work) and HG-CFE models to SP simulation. In theexample, the CFE and HG-CFE models are tested by comparing to asingle-porosity (SP) model for a water and CO2 injection strategyapplied in a 2 m×10 m column with four matrix blocks. The purpose is toverify that the same results may be obtained with models based onembodiments herein as with a single-porosity simulation, but with a muchreduced computer execution time. The reservoir is discretized into21×103 cells as shown in FIG. 8.1 . The dark lines are the fracturecells. The remaining horizontal and vertical lines are matrix blocks.The model is fully saturated with oil. The porosity and the permeabilityof the matrix are 0.15 and 4 md, respectively. In FIG. 8.1 , the thirdhorizontal row from the top (701) is the locations of the fracture cellsin each of the models. The original fracture aperture (a) is 5 mm with aporosity 1 and a permeability 4000 md. The CFE cell thickness (A) is 5.5cm i.e., 11 times the aperture of original fracture.

In the example of FIG. 8.1 , 2 injectors (703) and 2 producers (705) areillustrated by ellipses near the bottom and top, respectively. The wellsare completed in the fracture cells. Injectors are injecting water andCO2 with a reservoir rate of 0.003 rm3/d for 50 days and 125 days,respectively, and at a BHP limit of 500 bar. Producers are producing ata 0.003 rm3/d rate for 50 days at a BHP limit of 230 bar. Capillarypressures are neglected.

The CFE (this work) is compared to SP and traditional CFE models. Theoil saturation profiles is shown in FIG. 8.2 at 1 PV water injection.FIG. 8.2 shows that the improved CFE (this work) model gives much betterresults in comparison with the traditional CFE (literature), as theresults are closer to the SP model reference results on the left of FIG.8.2 . In other words, the SP model is deemed accurate. A comparison atthe end of the CO2 injection period shows similar behavior where CFE(this work) model gives more accurate results (not shown).

The same comparisons may be conducted to evaluate the results of HG-CFE(this work) model. As shown in FIG. 8.2 , FIG. 9 , and FIG. 10 , HG-CFEproduces a more accurate and efficient approximation as compared toother models when compared to the reference SP model.

As shown on the right-hand panel of FIG. 9 , the SP oil recover results(802) are quite close to the HG-CFE (this work) oil recovery results(808). The CFE (literature) results (804) and CFE (this work) results(806) are not as close to the SP model results (802). On the left-handside of FIG. 8 , the water cut results show that the SP model results(802) and the HG-CFE (this work) results (808) are extremely close. Thewater cut results for the CFE (this work) method 806 are closer to theSP results (802) than are the results for CFE (literature) (804).

FIG. 10 shows water saturation profiles at selected modeling blocks forthe SP model, CFE simulations (literature), CFE and HG-CFE simulations(this work). The results of the HG-CFE method (908) are quite close tothe reference SP model results (902). The water saturation profiles ofthe CFE (this work) (906) are closer to the SP model water saturationprofiles (902) than are the CFE (literature) profiles (904).

The HG-CFE model eliminates, in addition, grid construction effects nearfractures. Using Implicit Pressure Explicit Saturation (IMPES) andAdaptive Implicit Method (AIM) formulations, the simulation run timeimprovement is shown in graph (1100) in FIG. 11 . In FIGS. 11, 13, and15 , the x-axis has the timesteps of the simulation in terms of numberof days. Specifically, the x-axis indicates that the simulation hasidentified the fluid flow at the number of days from the starting time.The y-axis is the elapse time in terms of number of seconds that thecomputing system has executed the simulation. Thus, the y-axis is anindication of the number of computing resources used to be at thesimulated fluid flow time of the x-axis. The, time on the lines is theelapse time at a particular x-axis simulated time.

In FIG. 11 , the amount of time to compute the results are shown next tothe lines on the graph (e.g., 7 minutes and 13 minutes for HG-CFE andSP, respectively, for AIM, 22 minutes and 8 hours, 25 minutes for HG-CFEand SP, respectively, for IMPES). FIG. 11 shows that HG-CFE method is 2times faster than SP model for AIM, and 23 times faster for IMPES. TheCFE elements thickness is 11 times that of the original fractures. Thisis equivalent to CFE elements with only 2.5 times bigger pore volumethan original fracture cells, and this is in good agreement with thespeedup gained using HG-CFE using AIM scheme.

The next example is probably computationally too expensive for asingle-porosity simulation and demonstrates the reliability of HG-CFEmethod. The performance of HG-CFE and SP simulation in 3D complexreservoir uses the same fluid properties and with a more complex networkof fractures with fracture thickness of 1 mm. The reservoir dimensionsare 600 m×200 m×100 m, with a grid resolution 67×28×10, matrix cell of10 m×10 m×10 m, and fracture cell of 0.001 m×10 m×10 m. The matrixporosity and permeability are 0.15 and 1 md, respectively. The porosityand permeability in the fracture are, respectively, 1 and 10,000 md. Theratio matrix/fracture pore volume is 1000. In the example, the producerand injector are completed in the matrix cells (not shown). The injectorinjects water for 10 years and is controlled by reservoir rate at 200rm3/day with a BHP limit of 1000 bar. The producer produces for 10 yearswith a reservoir rate control of 200 rm3/day and a BHP limit of 50 bar.

Turning to FIG. 12 , a comparison (1200) with SP model and HG-CFE methodis performed using different CFE cell expansions of 101, 201, and 401times (e.g., volume expansion parameter values) to sensitize on both thenumerical results and computational complexity. As shown by the lines(1206, 1208) overlapping on both oil recover graph (1202) and the watercut graph (1204), the HG-CFE method gives very accurate results incomparison with the SP reference model. The difference in recovery withSP model for 101, 201 and 401 times larger CFE cells is 0.002%, 0.004%and 0.0065%, respectively. The results demonstrate that the HG-CFE modelis retaining a high accuracy while varying the CFE cell volumes. With asmaller CFE expansion, the HG-CFE converges exactly to SP model. Scalingthe relative permeability in the fracture to allow the correct amount ofwater to be initially mobile, the results are even more improved. TheHG-CFE with the correction reproduces the exact results of the SP modeldemonstrating the accuracy of the HG-CFE method. The water saturationprofiles also demonstrate a good agreement between the results of SPmodel and HG-CFE method with 401 times larger CFE cells.

The simulations run time for SP model and HG-CFE cases are shown in thegraph (1300) of FIG. 13 . In FIG. 13 , the amount of time to compute theresults using the corresponding technique are shown on the lines on thegraph. FIG. 13 shows that for 101, 201 and 401 CFE cell expansion,HG-CFE method is 153, 279 and 543 times faster than SP model. Thecomputational speedup of HG-CFE method with respect to the SP model forthe different CFE cell expansions is shown in graph (1400) of FIG. 14 .

An HG-CFE assessment in hydraulically fractured reservoir uses a 3Dmodel with a horizontal well that has 9 hydraulic fracture stages.Considering the fluid pumped along with proppant to fracture the well,the initial fluid saturations distribution may be considered in theapproximation of HG-CFE method. As initially, the hydraulic fracturesare fully saturated with water, the relative permeability curves in thefractures are adjusted as expanding fractures to CFE cells to providemore space for initial oil. Thus, when the production starts, oil isproduced along with the pumped water, which is not generally a realbehavior even if the volume of water pumped relative to oil reserves ismarginal.

To correct the inaccuracy as compared to real behavior, the fluidsaturations in the fractures may be calibrated to beS_(w)=1/PoreVolumeMultiplier, and S_(o)=1−S_(w). To achieve thecalibrations, the relative permeability in the fracture can be scaledwith critical oil saturation equal to 1−1/PoreVolumeMultiplier. Usingthe scaling factor will immobilize the oil portion initially in thefracture which is again marginal with respect to the oil initially inplace. A correction to the mobilized oil can be performed to account tothe part immobilized in the expanded CFE cells. In the example, the CFEmultiplier in thickness is 301, which means 4 times the pore volume ofthe original fractures and that leads to initial fluid saturations of0.25 water and 0.75 oil.

The strategy for the horizontal producer is 10 years' production withliquid rate control of 50 STB/day and a BHP limit of 600 psi. Theresults for the SP model and the HG-CFE method with 301 times CFE cellexpansion demonstrate agreement between the SP model and the HG-CFEmethod, as confirmed with previous examples. The HG-CFE method producesvery accurate results that matches the SP model. Finally, the simulationrun time as shown in graph (1400) of FIG. 15 reveals that, for thisexample, HG-CFE method is 14 times faster than SP model.

Embodiments may be implemented on a computing system. Any combination ofmobile, desktop, server, router, switch, embedded device, or other typesof hardware may be used. For example, as shown in FIG. 16.1 , thecomputing system (1600) may include one or more computer processors(1602), non-persistent storage (1604) (e.g., volatile memory, such asrandom access memory (RAM), cache memory), persistent storage (1606)(e.g., a hard disk, an optical drive such as a compact disk (CD) driveor digital versatile disk (DVD) drive, a flash memory, etc.), acommunication interface (1612) (e.g., Bluetooth interface, infraredinterface, network interface, optical interface, etc.), and numerousother elements and functionalities.

The computer processor(s) (1602) may be an integrated circuit forprocessing instructions. For example, the computer processor(s) may beone or more cores or micro-cores of a processor. The computing system(1600) may also include one or more input devices (1610), such as atouchscreen, keyboard, mouse, microphone, touchpad, electronic pen, orany other type of input device.

The communication interface (1612) may include an integrated circuit forconnecting the computing system (1600) to a network (not shown) (e.g., alocal area network (LAN), a wide area network (WAN) such as theInternet, mobile network, or any other type of network) and/or toanother device, such as another computing device.

Further, the computing system (1600) may include one or more outputdevices (1608), such as a screen (e.g., a liquid crystal display (LCD),a plasma display, touchscreen, cathode ray tube (CRT) monitor,projector, or other display device), a printer, external storage, or anyother output device. One or more of the output devices may be the sameor different from the input device(s). The input and output device(s)may be locally or remotely connected to the computer processor(s)(1602), non-persistent storage (1604), and persistent storage (1606).Many different types of computing systems exist, and the aforementionedinput and output device(s) may take other forms.

Software instructions in the form of computer readable program code toperform embodiments may be stored, in whole or in part, temporarily orpermanently, on a non-transitory computer readable medium such as a CD,DVD, storage device, a diskette, a tape, flash memory, physical memory,or any other computer readable storage medium. Specifically, thesoftware instructions may correspond to computer readable program codethat, when executed by a processor(s), is configured to perform one ormore embodiments.

The computing system (1600) in FIG. 16.1 may be connected to or be apart of a network. For example, as shown in FIG. 16.2 , the network(1620) may include multiple nodes (e.g., node X (1622), node Y (1624)).Each node may correspond to a computing system, such as the computingsystem shown in FIG. 16.1 , or a group of nodes combined may correspondto the computing system shown in FIG. 16.1 . By way of an example,embodiments may be implemented on a node of a distributed system that isconnected to other nodes. By way of another example, embodiments may beimplemented on a distributed computing system having multiple nodes,where each portion may be located on a different node within thedistributed computing system. Further, one or more elements of theaforementioned computing system (1600) may be located at a remotelocation and connected to the other elements over a network.

Although not shown in FIG. 16.2 , the node may correspond to a blade ina server chassis that is connected to other nodes via a backplane. Byway of another example, the node may correspond to a server in a datacenter. By way of another example, the node may correspond to a computerprocessor or micro-core of a computer processor with shared memoryand/or resources.

The nodes (e.g., node X (1622), node Y (1624)) in the network (1620) maybe configured to provide services for a client device (1626). Forexample, the nodes may be part of a cloud computing system. The nodesmay include functionality to receive requests from the client device(1626) and transmit responses to the client device (1626). The clientdevice (1626) may be a computing system, such as the computing systemshown in FIG. 16.1 . Further, the client device (826) may include and/orperform at least a portion of one or more embodiments.

The computing system or group of computing systems described in FIGS.16.1 and 16.2 may include functionality to perform a variety ofoperations disclosed herein. For example, the computing system(s) mayperform communication between processes on the same or different system.A variety of mechanisms, employing some form of active or passivecommunication, may facilitate the exchange of data between processes onthe same device. Examples representative of these inter-processcommunications include, but are not limited to, the implementation of afile, a signal, a socket, a message queue, a pipeline, a semaphore,shared memory, message passing, and a memory-mapped file. Furtherdetails pertaining to a couple of these non-limiting examples areprovided below.

Based on the client-server networking model, sockets may serve asinterfaces or communication channel end-points enabling bidirectionaldata transfer between processes on the same device. Foremost, followingthe client-server networking model, a server process (e.g., a processthat provides data) may create a first socket object. Next, the serverprocess binds the first socket object, thereby associating the firstsocket object with a unique name and/or address. After creating andbinding the first socket object, the server process then waits andlistens for incoming connection requests from one or more clientprocesses (e.g., processes that seek data). At this point, when a clientprocess wishes to obtain data from a server process, the client processstarts by creating a second socket object. The client process thenproceeds to generate a connection request that includes at least thesecond socket object and the unique name and/or address associated withthe first socket object. The client process then transmits theconnection request to the server process. Depending on availability, theserver process may accept the connection request, establishing acommunication channel with the client process, or the server process,busy in handling other operations, may queue the connection request in abuffer until server process is ready. An established connection informsthe client process that communications may commence. In response, theclient process may generate a data request specifying the data that theclient process wishes to obtain. The data request is subsequentlytransmitted to the server process. Upon receiving the data request, theserver process analyzes the request and gathers the requested data.Finally, the server process then generates a reply including at leastthe requested data and transmits the reply to the client process. Thedata may be transferred, more commonly, as datagrams or a stream ofcharacters (e.g., bytes).

Shared memory refers to the allocation of virtual memory space in orderto substantiate a mechanism for which data may be communicated and/oraccessed by multiple processes. In implementing shared memory, aninitializing process first creates a shareable segment in persistent ornon-persistent storage. Post creation, the initializing process thenmounts the shareable segment, subsequently mapping the shareable segmentinto the address space associated with the initializing process.Following the mounting, the initializing process proceeds to identifyand grant access permission to one or more authorized processes that mayalso write and read data to and from the shareable segment. Changes madeto the data in the shareable segment by one process may immediatelyaffect other processes, which are also linked to the shareable segment.Further, when one of the authorized processes accesses the shareablesegment, the shareable segment maps to the address space of thatauthorized process. Often, only one authorized process may mount theshareable segment, other than the initializing process, at any giventime.

Other techniques may be used to share data, such as the various datadescribed in the present application, between processes withoutdeparting from the scope. The processes may be part of the same ordifferent application and may execute on the same or different computingsystem.

Rather than or in addition to sharing data between processes, thecomputing system performing one or more embodiments may includefunctionality to receive data from a user. For example, in one or moreembodiments, a user may submit data via a graphical user interface (GUI)on the user device. Data may be submitted via the graphical userinterface by a user selecting one or more graphical user interfacewidgets or inserting text and other data into graphical user interfacewidgets using a touchpad, a keyboard, a mouse, or any other inputdevice. In response to selecting a particular item, informationregarding the particular item may be obtained from persistent ornon-persistent storage by the computer processor. Upon selection of theitem by the user, the contents of the obtained data regarding theparticular item may be displayed on the user device in response to theuser's selection.

By way of another example, a request to obtain data regarding theparticular item may be sent to a server operatively connected to theuser device through a network. For example, the user may select auniform resource locator (URL) link within a web client of the userdevice, thereby initiating a Hypertext Transfer Protocol (HTTP) or otherprotocol request being sent to the network host associated with the URL.In response to the request, the server may extract the data regardingthe particular selected item and send the data to the device thatinitiated the request. Once the user device has received the dataregarding the particular item, the contents of the received dataregarding the particular item may be displayed on the user device inresponse to the user's selection. Further to the above example, the datareceived from the server after selecting the URL link may provide a webpage in Hyper Text Markup Language (HTML) that may be rendered by theweb client and displayed on the user device.

Once data is obtained, such as by using techniques described above orfrom storage, the computing system, in performing one or moreembodiments, may extract one or more data items from the obtained data.For example, the extraction may be performed as follows by the computingsystem in FIG. 16.1 . First, the organizing pattern (e.g., grammar,schema, layout) of the data is determined, which may be based on one ormore of the following: position (e.g., bit or column position, Nth tokenin a data stream, etc.), attribute (where the attribute is associatedwith one or more values), or a hierarchical/tree structure (consistingof layers of nodes at different levels of detail-such as in nestedpacket headers or nested document sections). Then, the raw, unprocessedstream of data symbols is parsed, in the context of the organizingpattern, into a stream (or layered structure) of tokens (where eachtoken may have an associated token “type”).

Next, extraction criteria are used to extract one or more data itemsfrom the token stream or structure, where the extraction criteria areprocessed according to the organizing pattern to extract one or moretokens (or nodes from a layered structure). For position-based data, thetoken(s) at the position(s) identified by the extraction criteria areextracted. For attribute/value-based data, the token(s) and/or node(s)associated with the attribute(s) satisfying the extraction criteria areextracted. For hierarchical/layered data, the token(s) associated withthe node(s) matching the extraction criteria are extracted. Theextraction criteria may be as simple as an identifier string or may be aquery presented to a structured data repository (where the datarepository may be organized according to a database schema or dataformat, such as XML).

The extracted data may be used for further processing by the computingsystem. For example, the computing system of FIG. 16.1 , whileperforming one or more embodiments, may perform data comparison. Datacomparison may be used to compare two or more data values (e.g., A, B).For example, one or more embodiments may determine whether A>B, A=B,A!=B, A<B, etc. The comparison may be performed by submitting A, B, andan opcode specifying an operation related to the comparison into anarithmetic logic unit (ALU) (i.e., circuitry that performs arithmeticand/or bitwise logical operations on the two data values). The ALUoutputs the numerical result of the operation and/or one or more statusflags related to the numerical result. For example, the status flags mayindicate whether the numerical result is a positive number, a negativenumber, zero, etc. By selecting the proper opcode and then reading thenumerical results and/or status flags, the comparison may be executed.For example, in order to determine if A>B, B may be subtracted from A(i.e., A−B), and the status flags may be read to determine if the resultis positive (i.e., if A>B, then A−B>0). In one or more embodiments, Bmay be considered a threshold, and A is deemed to satisfy the thresholdif A=B or if A>B, as determined using the ALU. In one or moreembodiments, A and B may be vectors, and comparing A with B includescomparing the first element of vector A with the first element of vectorB, the second element of vector A with the second element of vector B,etc. In one or more embodiments, if A and B are strings, the binaryvalues of the strings may be compared.

The computing system in FIG. 16.1 may implement and/or be connected to adata repository. For example, one type of data repository is a database.A database is a collection of information configured for ease of dataretrieval, modification, re-organization, and deletion. DatabaseManagement System (DBMS) is a software application that provides aninterface for users to define, create, query, update, or administerdatabases.

The user, or software application, may submit a statement or query intothe DBMS. Then the DBMS interprets the statement. The statement may be aselect statement to request information, update statement, createstatement, delete statement, etc. Moreover, the statement may includeparameters that specify data, or data container (database, table,record, column, view, etc.), identifier(s), conditions (comparisonoperators), functions (e.g. join, full join, count, average, etc.), sort(e.g. ascending, descending), or others. The DBMS may execute thestatement. For example, the DBMS may access a memory buffer, a referenceor index a file for read, write, deletion, or any combination thereof,for responding to the statement. The DBMS may load the data frompersistent or non-persistent storage and perform computations to respondto the query. The DBMS may return the result(s) to the user or softwareapplication.

The computing system of FIG. 16.1 may include functionality to presentraw and/or processed data, such as results of comparisons and otherprocessing. For example, presenting data may be accomplished throughvarious presenting methods. Specifically, data may be presented througha user interface provided by a computing device. The user interface mayinclude a GUI that displays information on a display device, such as acomputer monitor or a touchscreen on a handheld computer device. The GUImay include various GUI widgets that organize what data is shown as wellas how data is presented to a user. Furthermore, the GUI may presentdata directly to the user, e.g., data presented as actual data valuesthrough text, or rendered by the computing device into a visualrepresentation of the data, such as through visualizing a data model.

For example, a GUI may first obtain a notification from a softwareapplication requesting that a particular data object be presented withinthe GUI. Next, the GUI may determine a data object type associated withthe particular data object, e.g., by obtaining data from a dataattribute within the data object that identifies the data object type.Then, the GUI may determine any rules designated for displaying thatdata object type, e.g., rules specified by a software framework for adata object class or according to any local parameters defined by theGUI for presenting that data object type. Finally, the GUI may obtaindata values from the particular data object and render a visualrepresentation of the data values within a display device according tothe designated rules for that data object type.

Data may also be presented through various audio methods. In particular,data may be rendered into an audio format and presented as sound throughone or more speakers operably connected to a computing device.

Data may also be presented to a user through haptic methods. Forexample, haptic methods may include vibrations or other physical signalsgenerated by the computing system. For example, data may be presented toa user using a vibration generated by a handheld computer device with apredefined duration and intensity of the vibration to communicate thedata.

The above description of functions present a few examples of functionsperformed by the computing system of FIG. 16.1 and the nodes and/orclient device in FIG. 16.2 . Other functions may be performed using oneor more embodiments.

While the above has been described with respect to a limited number ofembodiments, those skilled in the art, having benefit of thisdisclosure, will appreciate that other embodiments can be devised whichdo not depart from the scope as disclosed herein. Accordingly, the scopeshould be limited by the attached claims.

What is claimed is:
 1. A method for simulating fluid flow in a fracturedreservoir comprising: generating a hybrid grid model (HG model) bygenerating a grid for a fractured reservoir model comprising a fractureand a matrix to obtain a generated grid; modifying the hybrid grid modelto generate a hybrid grid cross flow equilibrium model (HG-CFE model),wherein modifying comprises: selecting a volume expansion parameter fora plurality of cross flow equilibrium elements, wherein the volumeexpansion parameter comprises an amount the fracture is expanded toinclude surrounding matrix elements of the matrix; generating theplurality of cross flow equilibrium elements based on the generated gridand the volume expansion parameter, the plurality of cross flowequilibrium elements comprising a plurality of physical properties,wherein generating the plurality of cross flow equilibrium elementsfurther comprises combining a portion of the fracture with a fraction ofneighboring matrix blocks on either side of the fracture, within avolume defined by the volume expansion parameter, into larger cross flowequilibrium elements, and wherein the plurality of cross flowequilibrium elements comprise the larger cross flow equilibriumelements; executing a sensitivity analysis with respect to a volume ofthe plurality of cross flow equilibrium elements without re-gridding thefractured reservoir model by integrating flow equations in cross-flowequilibrium elements, of the plurality of cross flow equilibriumelements, related to fracture-fracture flow; correcting inaccuracies bycalibrating fluid saturations in the fracture by scaling a relativepermeability in the fracture according to an oil saturation scalingfactor; and calculating, using the plurality of cross flow equilibriumelements, a plurality of pore volume and transmissibility multipliers;simulating, using the HG-CFE model, a fluid flow in the fracturedreservoir model by using the plurality of pore volume andtransmissibility multipliers and a fracture relative permeability curveto obtain a result, wherein the fluid flow is calculated for theplurality of cross flow equilibrium elements; and presenting the result.2. The method of claim 1, wherein the plurality of physical propertiescomprises a plurality of matrix and fracture properties of the fracturedreservoir.
 3. The method of claim 1, wherein generating the gridcomprises using at least one selected from a group consisting of a onedimensional fracture in a two dimensional fractured reservoir and a twodimensional fracture in a three dimensional fractured reservoir.
 4. Themethod of claim 1, wherein the volume expansion parameter is calculatedas a ratio of a selected fracture aperture to a cross flow equilibriumexpanded fracture.
 5. The method of claim 1, further comprising:selecting the plurality of physical properties for cross flowequilibrium elements from a group consisting of volume, porosity,permeability, net-to-gross, and transmissibility.
 6. The method of claim1, further comprising: calculating a fracture to fracturetransmissibility using a star-delta approach.
 7. The method of claim 1,further comprising: calculating the fluid flow from the matrix to thefracture using the fracture relative permeability curve.
 8. The methodof claim 1, further comprising: scaling a relative permeability in thefracture with oil saturation.
 9. The method of claim 1, whereinexecuting the sensitivity analysis uses a fracture relative permeabilitycurve.
 10. A system comprising: one or more processors; a memory;instructions stored in the memory and executable by at least one of theone or more processors to cause the system to: generate a hybrid gridmodel (HG model) by generating a grid for a fractured reservoir modelcomprising a fracture and a matrix to obtain a generated grid; modifythe hybrid grid model to generate a hybrid grid cross flow equilibriummodel (HG-CFE model), wherein modifying comprises: selecting a volumeexpansion parameter for a plurality of cross flow equilibrium elements,wherein the volume expansion parameter comprises an amount the fractureis expanded to include surrounding matrix elements of the matrix;generating the plurality of cross flow equilibrium elements based on thegenerated grid and the volume expansion parameter, the plurality ofcross flow equilibrium elements comprising a plurality of physicalproperties, wherein generating the plurality of cross flow equilibriumelements further comprises combining a portion of the fracture with afraction of neighboring matrix blocks on either side of the fracture,within a volume defined by the volume expansion parameter, into largercross flow equilibrium elements, and wherein the plurality of cross flowequilibrium elements comprise the larger cross flow equilibriumelements; and executing a sensitivity analysis with respect to a volumeof the plurality of cross flow equilibrium elements without re-griddingthe fractured reservoir model by integrating flow equations incross-flow equilibrium elements, of the plurality of cross flowequilibrium elements, related to fracture-fracture flow; correctinginaccuracies by calibrating fluid saturations in the fracture by scalinga relative permeability in the fracture according to an oil saturationscaling factor; and calculating, using the plurality of cross flowequilibrium elements, a plurality of pore volume and transmissibilitymultipliers; simulate, using the HG-CFE model, a fluid flow in thefractured reservoir model by using the plurality of pore volume andtransmissibility multipliers and a fracture relative permeability curveto obtain a result, wherein the fluid flow is calculated for theplurality of cross flow equilibrium elements; and present the result.11. The system of claim 10, wherein generating the grid comprises usingat least one selected from a group consisting of a one dimensionalfracture in a two dimensional fractured reservoir and a two dimensionalfracture in a three dimensional fractured reservoir.
 12. The system ofclaim 10, wherein the volume expansion parameter is calculated as aratio of a selected fracture aperture to a cross flow equilibriumexpanded fracture.
 13. The system of claim 10, wherein the instructionsfurther cause the system to: select the plurality of physical propertiesfor cross flow equilibrium elements from a group consisting of volume,porosity, permeability, net-to-gross, and transmissibility.
 14. Thesystem of claim 10, wherein the instructions further cause the systemto: calculate a fracture to fracture transmissibility using a star-deltaapproach.
 15. The system of claim 10, wherein the instructions furthercause the system to: calculate the fluid flow from the matrix to thefracture using the fracture relative permeability curve.
 16. The systemof claim 10, wherein the instructions further cause the system to: scalea relative permeability in the fracture with oil saturation.
 17. Acomputer program product comprising computer readable program code forcausing a computing system to perform operations, the operationscomprising: generating a hybrid grid model (HG model) by generating agrid for a fractured reservoir model comprising a fracture and a matrixto obtain a generated grid; modifying the hybrid grid model to generatea hybrid grid cross flow equilibrium model (HG-CFE model), whereinmodifying comprises: selecting a volume expansion parameter for aplurality of cross flow equilibrium elements, wherein the volumeexpansion parameter comprises an amount the fracture is expanded toinclude surrounding matrix elements of the matrix; generating theplurality of cross flow equilibrium elements based on the generated gridand the volume expansion parameter, the plurality of cross flowequilibrium elements comprising a plurality of physical properties,wherein generating the plurality of cross flow equilibrium elementsfurther comprises combining a portion of the fracture with a fraction ofneighboring matrix blocks on either side of the fracture, within avolume defined by the volume expansion parameter, into larger cross flowequilibrium elements, and wherein the plurality of cross flowequilibrium elements comprise the larger cross flow equilibriumelements; and executing a sensitivity analysis with respect to a volumeof the plurality of cross flow equilibrium elements without re-griddingthe fractured reservoir model by integrating flow equations incross-flow equilibrium elements, of the plurality of cross flowequilibrium elements, related to fracture-fracture flow; correctinginaccuracies by calibrating fluid saturations in the fracture by scalinga relative permeability in the fracture according to an oil saturationscaling factor; and calculating, using the plurality of cross flowequilibrium elements, a plurality of pore volume and transmissibilitymultipliers; simulating, using the HG-CFE model, a fluid flow in thefractured reservoir model by using the plurality of pore volume andtransmissibility multipliers and a fracture relative permeability curveto obtain a result, wherein the fluid flow is calculated for theplurality of cross flow equilibrium elements; and presenting the result.18. The computer program product of claim 17, wherein the plurality ofphysical properties comprises a plurality of matrix and fractureproperties of the fractured reservoir model.
 19. The computer programproduct of claim 17, wherein generating the grid comprises using atleast one selected from a group consisting of a one dimensional fracturein a two dimensional fractured reservoir and a two dimensional fracturein a three dimensional fractured reservoir.
 20. The computer programproduct of claim 17, wherein the volume expansion parameter iscalculated as a ratio of a selected fracture aperture to a cross flowequilibrium expanded fracture.